1. Field of the Invention
The present invention relates to a breast image obtaining method and apparatus for obtaining a radiographic breast image using a solid-state detector, or stimulable phosphor panel.
2. Description of the Related Art
In medical X-ray and other radiography, a system for reading out radiographic image information using a solid-state detector has conventionally been known as described, for example, in U.S. Pat. No. 6,268,614 and Japanese Unexamined Patent Publication No. 2000-284056, etc. The system uses a photoconductor made of, for example, an a-Se(amorphous selenium) plate which is sensitive to radioactive rays, including X-rays, as a solid-state detector in order to reduce an amount of dosage exposed to a subject, and improve diagnostic capabilities, an dreads out an electrostatic latent image, i.e., radiographic image information by irradiating recording radioactive rays (recording light), such as X-rays, carrying the radiographic image information on the solid-state detector to store the charges representing the latent image of the radiographic image information into the storage section of the solid-state detector, and thereafter scanning the solid-state detector with a reading electromagnetic wave (reading light), such as a laser beam, and detecting the current generated in the solid-state detector through flat or striped electrodes provided on both sides of the detector.
In medical X-ray and other radiography, a system for obtaining an image signal that carries radiographic image information using a stimulable phosphor panel is also known as described, for example, in U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-011395, etc. The system uses a stimulable phosphor panel capable of storing some of the radiation energy irradiated thereon, and thereafter emitting stimulated luminescence in proportion to the amount of energy stored when irradiated with excitation light, such as visible light, and obtains an image signal carrying radiographic image information by first recording radiographic image information of a subject, such as a human body, on the stimulable phosphor panel, and thereafter scanning the panel with excitation light, such as a laser beam, to generate stimulated luminescence, which is photoelectrically read out by a sensor.
Currently, a breast image obtaining apparatus for obtaining a radiographic image of a breast using an imaging device, including the solid-state detector, stimulable phosphor panel, and the like described above has been contemplated.
The breast image obtaining apparatus described above obtains a radiographic image of a breast by holding the breast of the subject on a photography platform having a solid-state detector and reading light source, or a stimulable phosphor panel, excitation light source, and sensor inside the housing, and irradiating radioactive rays from above the breast. This type of apparatus is required to have the capability to obtain the breast image information up to the area of the breast as close to the chest wall of the subject as possible.
For this reason, in the breast image obtaining apparatus, the imaging device, such as the solid-state detector, or stimulable phosphor panel is placed as close to the chest wall of a subject as possible inside the housing of the photography platform, and the imaging is carried out with the platform being pressed to the chest wall of the subject.
In reading out radiographic image information from the imaging device described above, the scanning rate of the scanning section of the reading light source, or the excitation light source and sensor must be constant. Otherwise, the image information may not be read out correctly due to variations in the density of the pixel. For this reason, the image information on the areas of the imaging device corresponding to the acceleration and deceleration zones of the scanning section may not be read out correctly. In the breast image obtaining apparatus described above, virtually no space is available between the inner wall of the housing and the end of the imaging device on the side of the subject, so that the image information on the imaging device close to the chest wall of the subject may not be readout correctly due to varied scanning rate, when the imaging device is sub-scanned in the direction perpendicular to the direction along the chest wall of the subject using a linear light source that irradiates linear light in the direction along the main scanning direction.
In addition, the intensity of the irradiating light (reading or excitation light) irradiated on the imaging device must be uniform across the imaging device. In scanning the imaging device with the linear light source described above, a linear light source which is slightly longer that the width of the imaging device in the main scanning direction is normally used, since the intensity of the irradiating light of the linear light source is not uniform at its ends. In the breast image obtaining system described above, however, the linear light source may not be extended further than the end of the imaging device on the side of the chest wall, if the imaging device is sub-scanned in the direction parallel to the direction along the chest wall, resulting in a different amount of light being irradiated on the end of the imaging device on the side of the chest wall and the image information thereof may not be read out correctly.